1. Field of the Invention
This invention relates to the manufacture of battery plates especially those of tubular type and is concerned in particular with the filling of the tubes of such plates, novel apparatus for carrying out the method and novel active material paste composition.
Tubular plates can have a variety of different types of tube material and tube configurations and can have tubes joined together or formed as separate tubes which are separately located on the spines.
One example of such separate tube arrangements utilizes woven fabric tubes having a thin outer plastic sheath provided with perforations about 1-2 mm across spaced apart by about 1 to 2 mms. The plastic sheath is about 0.1 to 0.2 mms thick.
The invention, though not limited to such arrangements, however is described with particular reference to tube arrangements in which the tubes are a single preformed assembly since this facilitates assembly of the tubes onto the spines of the plate.
2. Description of the Prior Art
A conventional method for making tubular plates involves impregnating fabric tubes with a resin to render them stiff though still permeable, locating the tubes on an array of lead alloy spines, one spine to each tube, and filling the space between the interior of the tubes and the spines with active material e.g. lead oxide powder from a hopper and shaking the assembly to compact the powder in the tube. This method has considerable problems including waste of lead oxide powder, inconsistency of filling weight, and unevenness of filling, the active material tending to become over consolidated at what is the bottom of the tubes during filling but is the top of the tubes in use.
One proposal, in G.B. Patent No. 947796, for reducing these problems was to extrude an active material paste containing a water soluble thickening agent into the tubes under high pressure. However, this method resulted in plates which had unpredictably variable electrical performance. There was also a tendency for the paste to break down and lose its fluidity under pressure and also to go solid inside the machinery if there were any intervals or delay in the production sequence.
Another proposal, in German Auslegeschrift No. 2243377 is to inject a metered volume, corresponding to the internal volume of the tubular plate, of an acidic automotive battery paste into the tubes within a very short space of time e.g. less than 1.5 seconds. The paste has a certain amount of additional water added to it. This is alleged to form a suspension but in fact this mixture is a thick paste which is not self levelling. The pastes which are disclosed contain 3 parts grey lead oxide, 1 part red lead oxide, 2.96 parts by weight of oxides to each part by weight of acid and water and 0.06 parts by weight of 1.4 specific gravity sulphuric acid for each part by weight of oxide, i.e. 12.6% of the grey lead oxide was sulphated. The specification decribes the pastes as having dynamic viscosities in the range 3000 to 4000 centipoises. No indication is given of what method of measurement of viscosity or measuring apparatus is to be used.
We have measured the viscosity of the above paste described in German Auslegeschrift No. 2243377 on a rotating vane viscometer as described below using the measurement technique described below.
We find that this paste has a rotating vane viscometer torque value (as defined herein) of 3.5 lbs ft. The paste is not self levelling; that is when a mass is deposited as a lump on a flat surface it does not assume a flat level surface within a period of 24 hours, though small amounts of liquids separate outfrom the solids during this period.
The process has the disadvantages of requiring accurate metering of the volume of paste to be injected and the paste is so viscous that it has to be forced into the tubes under high pressure.
This needs to use high pressure results in variation in density of the paste along the length of the tubes, the paste tending to become over consolidated at the inlets to the tubes which are the bottoms of the tubes in use. In addition it introduces difficulties in getting the paste to travel the full length of a tube, especially in a deep plate. This severely limits the size of plate which can be filled. This introduces further problems in production of batteries from the paste and in use of the batteries.
We have discovered that these problems can severally and collectively be reduced by using a radically different active material composition, apparatus and method in which a pourable liquid slurry of very low viscosity is poured or fed into the tubes under gravity and then, when the tubes are full, preferably consolidated by allowing the back pressure to build up. By controlling the value to which the back pressure is allowed to rise, the degree of consolidation can be varied as desired and a very even consolidation achieved.
The method of the present invention is described and claimed in corresponding U.S. Pat. No. 4,037,630 with the present application being a Divisional application thereof.
The apparatus for carrying out the method in accordance with the invention preferably comprises at least one filling station comprising means for supporting the envelope of a plate assembled on its current conducting element in a substantially vertical plane and a filling manifold adapted to introduce slurry into the envelope of a plate located in the said supporting means, the apparatus further comprising, a slurry storage tank provided with agitating means adapted to contain a supply of active material slurry, and delivery means for delivering the slurry from the storage tank to the manifold of a selected filling station wherein the plate comprises a plurality of tubular plate members.
The delivery means preferably include recirculating means for recirculating the slurry to the storage tank when the slurry is not being delivered to a filling station.
The delivery means may comprise a pump having an inlet pipe communicating with the storage tank and valve means, the recirculating valve, communicating with the outlet of the pump for directing, preferably selectively station, or when more than one station is used, to a selected station, or for recirculating the slurry to the storage tank.
The means for supporting the plates are preferably adapted to support tubular plates and comprise a frame rigidly secured to the filling manifold and carrying top and bottom clamps arranged to releaseably clamp the plate to the frame.
The clamps may be toothed and conform to the outside surface profile of the bottom and top of the tubular plate.
At least the top clamp is preferable provided with a resilient sealing liner.
The manifold of preferably adapted for use with tubular plates and then preferably has an outlet nozzle assembly consisting of rigid feed tubes spaced apart in a straight line with their centers on the centers of the tubes of the plate and having external diameters corresponding to the internal diameters of the tubes of the plate. Thus the tubes are preferably arranged vertically so that the slurry is introduced under gravity.
The feed tubes may extend through a resilient gasket, the dimensions of the frame in relation to the plate being such that the end of the plate has to be forced up into the gasket in order to locate the plate in the supporting means.
Preferably a pressure responsive valve is located in communication with the inlet side of each filling manifold.
Preferably at least two filling stations are provided for each pump and slurry storage tank and the recirculating valve is a three way valve.
The or each pressure responsive valve may be arranged to actuate automatic switching of the recirculating valve or the valve means connecting the or each manifold to the common feed pipe to the recirculating position and to release the pressure on the plate as soon as a preset pressure is reached.
The pump preferably comprises a rotor in the form of a single start helix fitting in a cylinder in the form of a double start helix of twice the pitch of the rotor, in which the rotor turns about its own axis in one direction, while its axis orbits about the axis of the cylinder in the opposite direction at the same speed.
In a further broader aspect of the invention the method is not restricted to the filling of tubular sheathed plates. Thus other shapes of sheath can be used, e.g. envelope shaped sheaths and in this case the grid need no longer be in the form of a comb of spines but could be a conventional cast grid or a reticulated plate, e.g. an expanded metal mesh or a sheet with apertures punched through it, it could even be a solid plate so long as the necessary current collecting function was adequately carried out.
The sheath can be of flexible material or of rigid or stiff material but at least when the sheath is flexible it is preferred to support its faces with porous support means, e.g. rigid foraminous sheets, meshes or grids during the filling operation so as to keep the plate substantially parallel sided while permitting the liquids to pass through.
With this arrangement the inlet manifold also has to be modified so that, instead of a row of tubes which plug into the ends of the individual tubes of the sheath, a single or double tubular slot is provided to plug into the open bottom end of the sheath. A double slot arrangement which nests over the end of the grid and affords a pair of slots extending along either side of the grid and can be clamped thereto may have advantages over a single slot arrangement.
The end of the sheath can be sealed with an elongated bottom bar after filling. This can consist of an internal plug gripping the end of the grid and an external clip or integral flange on the plug arranged to grip the outside of the envelope and hold it in against the plug.
In another alternative instead of an inlet manifold of fixed tubular outlets or fixed slots an arrangement of retractable filling tubes extending down into the sheath can be used. The arrangement would start with the filling tubes fully extended down into the sheath around the spines (which now need not have centering fins since the filling tubes perform this function). As the active material issues from the ends of the tubes the tubes are withdrawn up along the sheath and finally halt at the open top end of the sheath where they may be momentarily clamped and then released to complete filling of the plate.
Clearly however this arrangement is more complicated than the arrangement in which the slurry is merely fed in at the tops of the tubes and this simple arrangement is much preferred.